The present invention relates to a non-contact type liquid level sensor, and more particularly to a non-contact type liquid level sensor in which assembling of the liquid level sensor to a liquid storing tank is considerably improved by reducing the size of the liquid level sensor.
In the related non-contact type liquid level sensor, a detector is constructed with a resistor plate and a movable contact abutting on the resistor plate. When a float vertically moves with a change of a liquid level to be measured, the movable contact slides on and along the resistor plate to vary a resistance, and a liquid level is detected on the basis of a resistance change detected. In this type of the liquid level sensor, sometimes, the movable contact and the resistor plate are oxidized. Where those are oxidized, a variation of detected resistance value is extremely large or noise is generated. Thus, problem of detection accuracy to be solved is present.
To solve the problem of the liquid level sensor, a non-contact type liquid level sensor is proposed recently. The proposed liquid level sensor uses a magnetoelectric transducing element, which detects a change of magnetic force and converts the detected magnetic force into an electrical signal. The non-contact type liquid level sensor is disclosed in the journal of technical disclosure No. 2001-4678, issued by Japan Institute of Invention and Innovation.
An example of a related non-contact type liquid level sensor will be described with reference to FIGS. 13 to 15. FIG. 13 is a longitudinal sectional view showing a related non-contact type liquid level sensor 1, FIG. 14 is a perspective view showing a positional relationship among a magnetoelectric transducing element 11, a magnet 5, and a stator 9, which are extracted from FIG. 13, and FIG. 15 is an enlarged, longitudinal sectional view showing a structure when a magnet chamber cover 14 is mounted in a magnet chamber 2a. 
As shown in FIG. 13, the related non-contact type liquid level sensor 1 is arranged such that a sensor housing 2 made of synthetic resin is fixed to within a vehicle fuel tank 3. A rotary shaft 4 is rotatably disposed within a magnet chamber 2a formed within the sensor housing 2. A sintered magnet 5 is fit to an outer peripheral surface of the rotary shaft 4. The sintered magnet 5 is fastened to the rotary shaft 4 by fixing member, such as bonding or engagement.
The sintered magnet 5, for example, a ferrite magnet, is formed in a manner that magnetic powder is molded into an annular shape, and sintered, and then the resultant is radially magnetized to have two magnetic poles. As shown in FIG. 15, a magnet chamber cover 14 made of synthetic resin is fixed to an opening part of a magnet chamber 2a in a manner that pawls 2b formed in the sensor housing 2 are fit into locking holes 14a formed in the magnet chamber cover 14. A support hole 14b is formed in the magnet chamber cover 14. One end of the rotary shaft 4 is inserted into the support hole 14b and rotatably supported by the support hole.
As shown in FIG. 13, one end of a float arm 6 is mounted on a float 8, and the other end thereof is fastened to the rotary shaft 4. When the float 8 vertically moves with a change of a liquid level 15, a vertical movement of the float is transmitted through the float arm 6 to the rotary shaft 4 which in turn rotates.
As shown in FIG. 14, a couple of semicircular stators 9 are circularly arranged around the sintered magnet 5, while being confronted with an outer peripheral surface of the sintered magnet 5. A gap 10 is present between the first ends of the coupled stators 9, and another gap 10 is present between the second ends of the same. A phase difference of 180° is present between those gaps. A magnetoelectric transducing element 11, such as a Hall element or a Hall IC, is placed in one of the gaps, while being put between the coupled stators. Terminals 11a of the magnetoelectric transducing element 11 are electrically connected to a wiring board 12, which is electrically connected to a terminal 13.
When the float 8 vertically moves with a change of the liquid level 15, the rotary shaft 4 turns together with the sintered magnet 5. With the turn of the sintered magnet 5, a magnetic flux density passing through the magnetoelectric transducing element 11 changes. The magnetoelectric transducing element 11 detects a change of the magnetic flux density and converts the magnetic flux density change into an electrical signal.
The non-contact type liquid level sensor 1 has such a structure that a couple of semicircular stators 9, while being circularly arranged, are confronted with an outer peripheral surface of the annular sintered magnet 5. With presence of the circularly arranged stators 9, there is a limit in reducing the size of the non-contact type liquid level sensor 1. In particular, the non-contact type liquid level sensor 1 is frequently mounted onto a small reserve cup attached to the inside of a vehicle fuel tank 3. From the point of view of the assembling work improvement and securing a space of the vehicle fuel tank 3, how to reduce the size of the non-contact type liquid level sensor 1 is an important problem.